Here's a place where I can post my thoughts on new papers, provide updates on my projects, and post info that will eventually be on my website The Theropod Database - http://theropoddatabase.com/ . It will center on theropods, but may delve into other topics as well such as phylogenetics.

Thursday, January 8, 2015

"Madsenius" and "Wyomingraptor"

As part of the huge Allosaurus rehaul coming in my annual "New Years" (*cough* it's already January 8th *cough*) Database update, I looked over all proposed Morrison allosaurs. Two of the most mysterious are the nomina nuda "Madsenius" and "Wyomingraptor", but I think I have them figured out. Enjoy.

This name was published in the column 'Dr. Bob's Dinofacts' in response to a question from a reader (Anonymous, 1997). The author (possibly Bakker himself) suggested it for a Tate Geological Museum specimen currently labeled Allosaurus. From 1997 until 2006, the Tate Museum included a "Wyomingraptor" section in its exhibits page, stating Bakker has proposed that name for a new genus of allosaur found at Como Bluff including a photographed forelimb. In the PaleoWorld episode "Killer Raptors" (episode 7 of season 4) aired in 1997, Bakker claims the only theropod preserved in Nail Quarry is "Wyomingraptor" (though note this is untrue, as the "Brontoraptor" material was also found there). The material (three adults and numerous juvenile to adult teeth) was detailed in Bakker (1997) where he simply calls them Allosaurus. Hartman (DML, 2000) wrote that Bakker has been "attempting to erect a new genus of allosaur, which he dubs "Wyomingraptor." He has been using this name for some time, but recently has found a specimen he thinks is different enough from the type(s) to warrant generic distinction." Given Bakker's notoriety as a splitter, the Nail specimens are likely to just be Allosaurus fragilis in any case. The photographed forelimb is similar to A. fragilis USNM 4734 except for being more robust, at least in metacarpal I, phalanx II-1 and II-2. Indeed, the robust first metacarpal is similar Torvosaurus, though the elongate phalanx I-1, radius and ulna are not. The forelimb is stated to be a cast, so it's not certain how much is based on real Nail fossils. It's possible some elements were scaled incorrectly from other specimens or are complete fabrications. It's also possible some material such as metacarpal I actually comes from the "Brontoraptor" individuals and that the forelimb is a chimaera. Further evaluation awaits description of the Nail material, which has yet to be distinguished from Saurophaganax either.

Figure from Bakker (2000), which I think demonstrates his concept of "Madsenius trux", represented by the lower 'creosaur' skull of DINO 2560 (= UUVP 6000).

This name was orginally reported in a children's book (Lambert, 1990) as "a proposed new allosaurid theropod to be formally named and described." Olshevsky (1991) listed it under Allosauridae as a taxon "to be described from the Morrison Formation by R. T. Bakker; based on distinctive skull material and other remains previously referred to Allosaurus and Creosaurus." Williams (online, 2004) mentioned the combination "Madsenius trux", leading Olshevsky (online, 2004) to say "trux" "was to have been Bakker's original type species epithet for the as-yet-unpublished genus Madsenius. According to him, it fits Madsen as appropriately as it fits Madsenius" [etymology- Latin trux means "fierce, rough, savage, wild"].

While nothing else unique has been written regarding "Madsenius", I believe clues in the literature point to its probable identity. Since at least 1988, Bakker has proposed two kinds of Morrison allosaur, the classic short-snouted fragilis vs. long-snouted 'atrox' dichotomy. Bakker (2000) cited the latter species as "The creosaur-type allosaurid (unfortunately, the type of Creosaurus MARSH is, by itself, indeterminate): Dinosaur National Monument skeleton University of Utah UUVP 6000 ..." as opposed to "True Allosaurus MARSH: specimens from the type locality of Allosaurus fragilis MARSH - the skeleton United States National Museum USNM 4734 ..." In that paper, he stated "These two types of skulls are easy to tell apart from the quadrate, lower temporal fenestra, and depth of the mandible; however, I find it impossible to separate the two taxa from isolated snout bones or post-crania." This matches the "distinctive skull material" noted by Olshevsky, and the 'long-snouted' skulls have been referred to both Allosaurus and Creosaurus by different workers, also matching Olshevsky's comment. Furthermore, UUVP 6000 (later recatalogued as DINO 2560) was the basis of Madsen's (1976) classic Allosaurus monograph and "Madsenius" clearly refers to Madsen. Putting everything together, I think it's apparent "Madsenius" was to be Bakker's name for creosaur-type allosaurs when he realized the Creosaurus holotype couldn't be assigned to either variety. UUVP 6000 was probably supposed to be the holotype.

If we accept this explanation, Bakker's characters supporting "Madsenius" can be evaluated. Bakker states the ventral quadrate angles posteriorly in DINO 2560, forming a deeply concave posterior edge to the element unlike A. fragilis AMNH 600. The posterior angle formed by the dorsal and ventral quadrate edges is 24 degrees in AMNH 600 compared to 30 degrees in the UUVP coll. quadrate illustrated by Madsen and 27 degrees in his cranial reconstruction of DINO 2560. Bakker's DINO 2560 illustration shows an unprecedented angle of 52 degrees. Angles in other specimens are 18 (AMNH 30798), about 44 (BYU 571/8901), 30 (DINO 11541), 43 (MOR 693), 15 (SMA 005/02) and 34 degrees (USNM 4734). For the laterotemporal fenestra, Bakker states the restriction caused by the ventral squamosal process is greater in A. fragilis AMNH 600 (least anteroposterior length of fenestra 15% of dorsoventral height) than DINO 2560 (26% in Madsen's reconstruction, 28% in Bakker's). Measurements in other specimens are about 25% (AMNH 666), 31% (AMNH 30798), < 24% (BYU 571/8901), 38% (DINO 11541), 20% (ML 415), 40% (MOR 693), 38% (SMA 005/02) and 16% (USNM 4734). Mandibular depth is 19% of length in Bakker's DINO 2560 (similar to 19% in Madsen's reconstruction) and 24% in his A. fragilis illustration, though the latter is a composite between AMNH 666 (which has only a partial surangular) and 5753 (which does not include mandibular elements). So even this minor 5% difference cannot be determined. Values in other specimens are about 19% (AMNH 30798), about 21% (BYU 571/8901), 17% (DINO 11541), 19% (MOR 693) and 20% (SMA 005/02). The above comparison suggests mandibular depth is fairly constant in known allosaurids, though quadrate angling and laterotemporal fenestra proportions vary widely. Yet importantly, the latter conditions both exhibit intermediates instead of two distinct clusters, and do not covary- AMNH 30798 and SMA 00/02 have low quadrate angles but wide laterotemporal fenestrae, while USNM 4734 has a high angle but restricted fenestra. Note neither of these conditions vary with stratigraphy either, and indeed the A. fragilis types and DINO 2560 are both from the Brushy Basin Member. Nor does it vary geographically, with Wyoming specimens encompassing almost the entirity of the variation. Based on this study then, "Madsenius" can be considered a synonym of Allosaurus fragilis and another example of Bakker's notorious splitting.

Bakker, 1997. Raptor family values: Allosaur parents brought great carcasses into their lair to feed their young. In Wolberg, Sump and Rosenberg (eds). Dinofest International, Proceedings of a Symposium, Academy of Natural Sciences. 51-63.